1. Field of the Invention
The invention concerns a hydraulic drive system with an initial partial system and a second partial system, where the partial system encompass a pump regulated by the stream required and hydraulic energy consumers connected to its output line, as well as a load pressure line carrying the maximum load pressure, and where a coupling device is provided for connecting the output line and the load pressure line of the first partial system with the output line and the load pressure line of the second partial system.
2. Description of the Art
Such a drive system is described in the DE-OS 31 46 508. The two partial systems are automatically coupled to a single-circuit system as soon as the useful stream of pressure medium in the one partial system is greater than the maximum useful stream available of the pump of this partial system. The coupling and separation occur exclusively as a function of the pressure gradient at the multiway valve assigned to the consumer actuated and controlling its direction and speed of movement. It makes no difference here which consumer is actuated. This can, however, be disadvantageous in some cases, e.g. if in the hydraulic drive system of an excavator the first partial system that handles the consumer required for raising and lowering the excavator column and the second partial system is provided for the filling and emptying movement of the excavator shovel. When the column is raised and shovel is emptied, the consumer assigned to the shovel will have only a slight load pressure, but a high rate of movement. On the other hand, the load pressure of the consumer assigned to the column is considerably higher and the rate of movement is considerably less. Thus, a specific consumer driven by the first partial system may have operating requirements which are different than the operating requirements of a consumer driven by the second partial system. If both partial systems are coupled, a high pressure level will prevail in the feed lines as a whole and correspondingly the total feed quantity determined by this high pressure level will be less at a constant hydraulic power output than when the pumps are operated individually. The proportion of transition power to the hydraulic power output, i.e., of the proportion of power manifested as fluid volume stream, is thus smaller after coupling; on the other hand, the power proportion that is manifested as pressure is greater. However, the oil leakage and pressure losses are thus also higher.
The present invention proposes to offer a hydraulic drive system of the above type, with which a higher transition or turnover power is attainable.